From a26aca2fe6dfe90693d0c41022d6308bb3ab4904 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Michael=20Tesa=C5=99?= <michael_tesar@icloud.com>
Date: Tue, 15 Sep 2026 22:28:53 +0200
Subject: [PATCH] fix constant bit_field field access returning zero value

---
 src/check_expr.cpp                 |  2 +-
 tests/internal/test_bit_field.odin | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/check_expr.cpp b/src/check_expr.cpp
index 891e4093a..aa62a6114 100644
--- a/src/check_expr.cpp
+++ b/src/check_expr.cpp
@@ -5600,7 +5600,7 @@ gb_internal ExactValue get_constant_field_single(CheckerContext *c, ExactValue v
 				if (success_) *success_ = false;
 				if (finish_) *finish_ = true;
 				return empty_exact_value;
-			} else if (is_type_struct(node->tav.type)) {
+			} else if (is_type_struct(node->tav.type) || is_type_bit_field(node->tav.type)) {
 				bool found = false;
 				for (Ast *elem : cl->elems) {
 					if (elem->kind != Ast_FieldValue) {
diff --git a/tests/internal/test_bit_field.odin b/tests/internal/test_bit_field.odin
index 40000b16e..71e77c3e0 100644
--- a/tests/internal/test_bit_field.odin
+++ b/tests/internal/test_bit_field.odin
@@ -171,3 +171,28 @@ bit_field_full_width_fields :: proc(t: ^testing.T) {
 	h.hi = 0
 	testing.expect_value(t, transmute(u64)h, 0xCAFE_F00D)
 }
+
+// field access on a constant bit_field used to always return the zero value
+@(test)
+bit_field_constant_field_access :: proc(t: ^testing.T) {
+	BF :: bit_field u32 { a: u8 | 3, b: u16 | 9, c: bool | 1, d: u8 | 7 }
+
+	FULL :: BF{ a = 3, b = 100, c = true, d = 5 }
+	testing.expect_value(t, FULL.a, u8(3))
+	testing.expect_value(t, FULL.b, u16(100))
+	testing.expect_value(t, FULL.c, true)
+	testing.expect_value(t, FULL.d, u8(5))
+
+	// unset fields still read as zero
+	EMPTY :: BF{}
+	testing.expect_value(t, EMPTY.a, u8(0))
+	testing.expect_value(t, EMPTY.b, u16(0))
+	testing.expect_value(t, EMPTY.c, false)
+	testing.expect_value(t, EMPTY.d, u8(0))
+
+	v := FULL
+	testing.expect_value(t, v.a, FULL.a)
+	testing.expect_value(t, v.b, FULL.b)
+	testing.expect_value(t, v.c, FULL.c)
+	testing.expect_value(t, v.d, FULL.d)
+}